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An Environmental Restoration Strategy in the Mountains Supplying Cape Town Shows How Removing Certain Invasive Trees Can Alter the Water Balance and Return Billions of Liters to the Supply System.
Cutting down trees to obtain more water may seem contradictory, but an ongoing operation in the mountains supplying Cape Town shows why this logic works when the removed vegetation is invasive.
Since April 2019, teams have removed exotic plants from tens of thousands of hectares, and according to the city government, this intervention now accounts for approximately 18.77 billion liters of additional water per year.
That volume is equivalent to about 51 million liters per day.
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This water is not artificially produced nor stored in a new reservoir.
The gain occurs because invasive pine, eucalyptus, and acacia trees consume more water than native vegetation and reduce the amount that reaches rivers, dams, and groundwater systems.
The current figure also helps update the scale presented in the title.
In October 2023, The Nature Conservancy estimated that the initiative was already recovering about 15.2 billion liters per year.
In March 2026, Cape Town raised that estimate to 18.77 billion liters annually.
The strategy gained traction following the water crisis that nearly brought the South African metropolis to the so-called “Day Zero” in 2018, when officials prepared for the possibility of cutting off regular residential water supply.
Since then, the recovery of watersheds has become part of a broader set of measures to reduce the city’s vulnerability to new droughts.
Invasive Trees Altered the Water Balance of the Mountains
The mountainous region surrounding Cape Town is home to fynbos, native vegetation primarily composed of shrubs adapted to the Mediterranean climate of southern Africa.
However, during the 19th and 20th centuries, foreign species were introduced for various purposes, including timber production.
These included pines, eucalyptus, and acacias, commonly referred to locally as pine, gum, and wattle.
Some of these trees escaped from the areas where they were planted and began to occupy slopes, valleys, and catchment areas.
The problem lies not simply in them being trees.
The issue is that some of these species grow rapidly, develop extensive roots, and consume water at rates far exceeding that of the native vegetation they replace.
Water absorbed by the vegetation partially returns to the atmosphere through evapotranspiration.
When large and water-intensive species occupy areas that were originally dominated by smaller plants adapted to relatively dry environments, less water remains available to feed streams, reservoirs, and groundwater recharge.
This is why removing certain trees can increase water availability, although the same reasoning cannot be indiscriminately applied to native forests.
Over 41,000 Hectares Received Initial Cleanup
On March 17, 2026, Cape Town reported that 41,306 hectares of invasive exotic plants have been removed since April 2019 in the sub-catchments deemed priority areas for the supply of major metropolitan reservoirs.
The work doesn’t end when a tree is cut down.
Many invasive species produce large quantities of seeds, and new sprouts may appear after the initial intervention.
Therefore, teams return to the treated areas.
During the same period, 50,644 hectares of follow-up operations were recorded, primarily aimed at controlling regrowth and new seedlings and preventing invasive vegetation from reclaiming lost space.
These figures do not necessarily mean that 91,950 different hectares have been cleared.
Some areas are counted more than once because a section may require maintenance after the initial removal.
Repetition is crucial to ensure that the water benefits do not vanish a few years later.
Teams Use Ropes to Reach Trees on Steep Slopes
Some priority areas are located in mountainous regions that are hard to access.
The Nature Conservancy reports operations where specialists trained in working at heights must venture into the mountains, staying in the field for several days and using ropes to reach pine trees located on steep slopes.
In certain spots, teams and equipment are transported by helicopter.
The challenge is precisely to remove trees capable of spreading seeds over long distances in terrains where conventional machinery cannot operate.
The project focuses efforts on different catchments in the Cape Mountains that feed reservoirs used by the metropolitan area.
The goal originally outlined by the Greater Cape Town Water Fund encompassed 54,300 hectares in seven priority catchment areas.
The urgency became evident during the severe drought that hit Cape Town between 2015 and 2018.
Reservoir levels dropped so low that the municipality developed plans for the so-called “Day Zero”, the point at which the conventional residential supply system could be severely restricted.
This extreme scenario, however, did not materialize.
Strict consumption restrictions, reduced water use for agriculture, new supply sources, and the return of rainfall allowed the city to escape the worst-case scenario.
The crisis, nonetheless, exposed the dependency on reservoirs and accelerated the search for alternatives.
It was in this context that, at the end of 2018, the Greater Cape Town Water Fund emerged, a partnership that brings together the public sector, environmental organizations, private funders, and other participants.
The initiative is led by The Nature Conservancy in collaboration with conservation partners, while Cape Town participates in operations through its Water and Sanitation Directorate.
Recovering Water Without Building a New Dam
Economic logic was one of the reasons the strategy gained international attention.
A study conducted for the Greater Cape Town Water Fund in 2018 concluded that restoring catchment areas through the removal of invasive species could be several times cheaper, per cubic meter obtained, than certain heavy infrastructure alternatives.
The comparison involves very different approaches.
A desalination plant requires construction, treatment systems, and energy to convert seawater into potable water.
Wells depend on the availability and management of aquifers.
New dams require suitable locations, licensing, substantial investments, and years of construction.
The removal of invasive species aims to act before this.
Instead of creating a new source, the goal is to prevent some of the existing water from being lost before it reaches the system.
This does not mean that Cape Town is betting exclusively on the mountains.
The municipal government itself states that the recovery of watersheds complements projects for extracting groundwater, controlled aquifer recharge, treated water reuse, and future desalination initiatives within the New Water Programme.
Researchers compare areas and monitor river responses following the removal of invasive species to verify if the gains predicted in models actually manifest in the environment.
According to the organization, these measurements support the hypothesis that the removal of these species increases the available flow.
Thus, the term “recover water” technically means, reducing a loss caused by invasive vegetation and increasing the volume that remains in the hydrological system.
Estimates increased from 15.2 to 18.77 billion liters per year
The results have improved as new areas have undergone intervention.
The Nature Conservancy reported that by October 2023, over 46,000 hectares had been treated within the broader program, with the calculated benefit reaching about 15.2 billion liters annually, or 42 million liters per day.
The official update from the municipality, published in March 2026, indicates 18.77 billion liters per year and approximately 51 million liters per day.
Differences in the number of hectares reported in various reports stem from the analyzed period, the type of operation counted, and the scope of each program.
The integrated annual report for 2024/25 from Cape Town, for example, recorded 63,000 hectares of invasive vegetation removed under its monitoring, with an estimated return of 48 million liters per day to the system.
For the most recent specific data regarding the effort published in March 2026, the municipality cites 18.77 billion liters per year.
Without control, invasive species could consume even more water
The problem could worsen if the plants were left unmanaged.
Previous studies from Cape Town estimated that the expansion of invasives had already significantly reduced the amount of water reaching rivers and reservoirs, and that losses would increase with the advance of these species.
The feasibility study of the Water Fund projected that the removal of invasives in priority areas could recover tens of billions of liters per year throughout the program.
The initial estimate reached approximately 55 billion liters annually in the early years, with the potential for even greater long-term benefits if the areas remained free of invasive species.
These projections should not be confused with the results already achieved.
The 18.77 billion liters per year reported for 2026 represents the benefit calculated in the current phase, while figures like 55 billion or 100 billion correspond to projected scenarios for a broader and more continuous deployment.
